HONG KONG (AP) — Hong Kong university student leaders said Thursday they’ll call for a boycott of the start of classes to pressure the government to respond to the protest movement gripping the city since June.

Student union leaders from 10 universities said they want students to skip the first two weeks of classes in September. They vowed to escalate their action if the city’s Beijing-backed leader, Carrie Lam, fails to respond by Sept. 13.

Young people have been at the forefront of the Chinese city’s protest movement, which was sparked by calls for the withdrawal of an unpopular extradition bill.

The bill, which would have allowed suspects to be extradited to mainland China where the judiciary is not independent, was eventually shelved but the crisis has since spiraled and supporters now have four other demands, including full democracy.

“Two weeks should be enough for the government to really think through how to respond to the five demands,” said Davin Wong, acting president of the Hong Kong University Students’ Union. The student leaders said they haven’t decided how to step up their action after the first two weeks, but it could include an open-ended general strike.

Also Thursday, high school students thronged a downtown square for a rally. Hundreds of teenagers, wearing black and holding umbrellas in the oppressive heat, chanted “Liberate Hong Kong” and “Revolution of our times” and called for Lam to step down, before breaking into groups to discuss the city’s political future.

Separately, major Hong Kong banks condemned the violence, while world diamond trading centers urged the postponement of an upcoming jewelry fair in the city, underscoring global corporate concerns about the movement’s impact on the Asian business center.

The banks took out advertisements in some newspapers calling for an end to the political crisis, signaling the financial industry’s support for Lam.

HSBC called for dialogue to resolve differences in a full page ad in the pro-Beijing Wen Wei Po.

“We are very concerned about recent social events and strongly condemn any violence and behavior undermining social order,” the bank said, adding it “fully supports a peaceful approach to finding solutions.”

Standard Chartered said it opposes violence and “firmly supports” the Hong Kong government in effectively maintaining social order.

Bank of East Asia took out a smaller ad with a similar message.

Diamond trading centers in Belgium, India and Israel called on the organizers of a major Hong Kong jewelry fair to postpone the event because of concerns about the security of diamond shipments and staff safety.

In a letter, they told the organizer, Informa Markets, that “you cannot, in good conscience expect us or the exhibitors to not only risk their goods, but the wellbeing and safety of their employees.”

The centers say that 30%-40% of exhibitors want the fair canceled even if the protests die down. They also fear that the jewelry might not be insured in case of riots.

Separately, police said two people have been charged with rioting in connection with a violent, indiscriminate attack on protesters.

Masked assailants suspected of ties to organized crime swung bamboo poles and steel rods in the rampage that left 45 people injured and came as a shocking escalation of the city’s summer of protest.

Protesters have complained about the lack of police progress in investigating the attack, which left both protesters and bystanders injured. They’ve accused police of colluding with the attackers by delaying their response, which police deny.

The charges are the first to be filed against the 28 people arrested after the attack.

Chief Superintendent Tse Chun-chung said police are awaiting legal advice from the Department of Justice on charges for the other 26.